Grounding For Profibus-DP network devices


Thread Starter

Mohamed Faizy

We have CS3000 DCS using ALP111 interface with SIMOCODE PRO C Starters and are suffering from Spurious trips from time to time. Based on analysis by Profibus n/w specialists baudrate set at DCS and SIMOCODE end seems to be on higher side (1.5kbps) and SIMOCODEs are not able to respond within a stipulated time period.

As a short term action baudrate brought down to 187.5Kbps and found significant improvement. As a long term action recommended by auditor introduced procentec n/w hubs and ensured siemens fast connect cables and connectors in addition to maintaining the cable looping/ spacing.

Of late again the same problems repeated and while checking it came to know that DCS Equipment and SIMOCDES are connected to a Non isolated Earthing circuit (Connected to Plant Equipment Earth) and we suspect this also could be a contributing factor. As i understand that Yokogawa DCS systems require an isolated Earth (<100ohm independent grounding from other Equipments) though. what could be the recommendations/guide lines from International Standard bodies if different systems interfaces through profibus like n/w.

Someone pl. reply to me ,
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What are you calling spurious trips? Are you loosing communications with other Simocodes? If so for how long. I have seen a problem where the the Yokogawa master looses communications with all the slave on the network for approx. 20 seconds. In looking at the messaging there is two consecutive messages that are 16 seconds apart with the next 8+ seconds where the master looks like it is starting back up.

Could this be what you are experiencing?

I wish I had a solution for you but I haven't figured this out yet. When I do I will post it.